The rapid development of data communication brings information explosion, and results in tremendous growth in demand for transport network bandwidth. The optical fiber communication has characteristics of large capacity and high bandwidth, and thus becomes a relatively good solution to provide the transport network bandwidth. SONET/SDH technologies have been already accepted as a mature standard of transport networks. Conventionally, backbone networks used for high-speed transport are all based on the SONET/SDH technologies.
However, the primary disadvantage of the SONET/SDH network is that it has been optimized for TDM (Time Division Multiplexing) services. Its protocols lack the function of effective management of services other than conventional voice services that are based on the TDM technologies. On the other hand, the viability of the SONET/SDH network has to be guaranteed by a protection circuit. Although the protection circuit provides an excellent ability of fault correction in a very short time, it consumes considerable bandwidth. The bandwidth trunk line is not flexible, and the entire loop has to run at the same rate. More importantly, an optical-electrical-optical conversion is required at each SONET/SDH node, which further increases the complexity of devices. Therefore, the SONET/SDH network has an inherent limitation in terms of management and support for an optical network with large bandwidth.
In order to support a larger transport network bandwidth, the further development of optimal fiber communication has adopted the technology of Wavelength Division Multiplexing to compose a DWDM (Dense Wavelength Derision Multiplexing) optical transport network. This DWDM optical transport network not only increases transport capacity, but also has the potential and practical value of networking. However, the DWDM optical transport network can not serve as the next generation transport network due to its own disadvantages, such as a weak supervision capability, poor scheduling and networking capabilities. Consequently, the OTN (Optical Transport Network) came into being as the architecture of next generation transport network.
Generally, the OTN is defined as an optical network with advanced features, such as optical channel routing, switching, supervising and viability, and is capable of transmitting various client signals in a flexible, extendible and reliable way with a larger bandwidth granularity (up to a maximum of tens of Gbps per optical channel). In the OTN with full functions, the transport network functions will transits from the SONET/SDH network to the OTN, and supply features of the service layer to satisfy demands of various fundamental devices and special services.
At present, one hot issue concerning the OTN is the building of Metropolitan Area Network. For building the metropolitan area network with the use of the OTN, it may be relatively ideal to network at a 10G rate level taking the network bandwidth into consideration. However, taking the optical performance into consideration, the networking at the 10G rate level has more problems than at a 2.5G rate level, e.g, significant optical attenuation, dispersion, etc., which would greatly decrease the distance between sites and accordingly increase the network investment cost. Consequently, the networking at a 5G rate level can get a compromise between the bandwidth and the investment cost to some extent.
Currently, only transport modes for client signals at three constant-bit-rate rate levels of CBR2G5, CBR10G, CBR40G have been defined in G.709 Protocol of the OTN standard established by the ITU-T (International Telecommunication Union Telecommunication) Standardization Sector, but no relevant definition has been provided for direct transport of CBR5G granular signals in the OTN.
For transporting the CBR5G signals through the OTN, the following two main solutions are conventionally adopted in the prior art.
The first solution utilizes the virtual cascade technology, and adopts the OPU1-2V to transport CBR5G signals though the virtual cascade of the OPU1's. Referring to FIG. 1, the method mainly includes the following steps:
First, with the use of the virtual cascading link technology, the CBR5G is mapped to a OPU1-2V frame to which OPU1-2VOH is added to form a frame in 2×3810×4 format.
Then, the frame is divided into an odd timeslot and an even timeslot, each composing an integrated OPU1.
Finally, the two OPU1s loaded with the CBR5G signals are mapped to two tributaries of ODU1/OTU1 which are transported through the OTN respectively through different routes.
The above solution in the prior art utilizes the virtual cascade technology to transport the CBR5G signals with the use of a 2×2.5G channel in the OTN, and hence can not implement directly the scheduling, supervision and management for the CBR5G granularity. In addition, it may cause different delays because the two 2.5G transport channels may run along different routes. Furthermore, in order to ensure that a sender and a receiver can both transmit and receive signals effectively, the sender and the receiver have to perform relatively complex processing on the virtual cascade protocol, and thus this solution is disadvantageous due to its high implementation cost.
The other solution in the prior art utilizes the OPU2 to transport the CBR5G signals, that is, loads the CBR5G signals to an OPU2 container for transport. Because the OPU2 is a 10G container, it can accommodate the CBR5G service. In a particular implementation, if the OPU2 container accommodates two CBR5G signals, these two CBR5G signals can be scheduled on the transport network as one granularity. Since the transport network merely can provide management and supervision for this one granularity, the two CBR5G signals being as two independent access sub-rates can't be scheduled, monitored or managed directly through the transport network overhead.
If the OPU2 container accommodates only one CBR5G signal, then the CBR5G signal has to be adapted to the OPU2, that is, data encapsulation and rate adaptation have to be performed on the CBR5G signal. Moreover, the 10G bearing capacity of the OPU2 only bears 5G services effectively, so the utilization of the container for an access node would be decreased greatly. Since there is no convergence mechanism, the utilization of bandwidth over the entire transport network may only be 50%, and thus the utilization of network bandwidth effectiveness may also be low.